1. Field of the Invention
The present invention relates to a layered chip package that includes a plurality of semiconductor chips stacked, and to a method of manufacturing the same.
2. Description of the Related Art
In recent years, lighter weight and higher performance have been demanded of portable devices typified by cellular phones and notebook personal computers. Accordingly, there has been a need for higher integration of electronic components for use in the portable devices. With the development of image- and video-related equipment such as digital cameras and video recorders, semiconductor memories of larger capacity and higher integration have also been demanded.
As an example of highly integrated electronic components, a system-in-package (hereinafter referred to as SiP), especially an SiP utilizing a three-dimensional packaging technology for stacking a plurality of semiconductor chips, has attracting attention in recent years. In the present application, a package that includes a plurality of semiconductor chips (hereinafter, also simply referred to as chips) stacked is called a layered chip package. Since the layered chip package allows a reduction in wiring length, it provides the advantage of allowing quick circuit operation and a reduced stray capacitance of the wiring, as well as the advantage of allowing higher integration.
Major examples of the three-dimensional packaging technology for fabricating a layered chip package include a wire bonding method and a through electrode method. The wire bonding method stacks a plurality of chips on a substrate and connects a plurality of electrodes formed on each chip to external connecting terminals formed on the substrate by wire bonding. The through electrode method forms a plurality of through electrodes in each of chips to be stacked and wires the chips together by using the through electrodes.
U.S. Patent Application Publication No. US 2008/0179728 A1 describes a laminated memory formed using the through electrode method.
JP-A-2003-163324 describes a three-dimensional laminated semiconductor device in which a plurality of chips stacked are wired by using wiring plugs that are similar to through electrodes. The three-dimensional laminated semiconductor device includes a stack of a plurality of unit semiconductor devices. Each single unit semiconductor device includes a semiconductor chip having a chip electrode, a wiring pattern, molding resin, and wiring plugs. The chip electrode is mounted on one surface of the wiring pattern. The molding resin covers the semiconductor chip and the wiring pattern. The wiring plugs penetrate the molding resin outside the semiconductor chip. The wiring plugs each have one end in contact with the one surface of the wiring pattern, and the other end exposed from the molding resin. The other surface of the wiring pattern is exposed in the surface of the molding resin. In the three-dimensional laminated semiconductor device, the wiring plugs of the lower one of two unit semiconductor devices are put into contact with the exposed surface of the wiring pattern of the upper one of the two unit semiconductor devices, whereby the plurality of semiconductor chips are wired together.
The wire bonding method has the problem that it is difficult to reduce the distance between the electrodes so as to avoid contact between the wires, and the problem that the high resistances of the wires hamper quick circuit operation. The through electrode method eliminates the above problems with the wire bonding method.
For a wafer to be cut into a plurality of chips, the yield of the chips, that is, the rate of conforming chips with respect to all chips obtained from the wafer, is 90% to 99% in many cases. Since a layered chip package includes a plurality of chips, the rate of layered chip packages in which all of the plurality of chips are conforming ones is lower than the yield of the chips. The larger the number of chips included in each layered chip package, the lower the rate of layered chip packages in which all of the chips are conforming ones.
A case will now be considered where a layered chip package is used to form a memory device such as a flash memory. For a memory device such as a flash memory, a redundancy technique of replacing a defective column of memory cells with a redundant column of memory cells is typically employed so that the memory device can normally function even when some memory cells are defective. The redundancy technique can also be employed in the case of forming a memory device using a layered chip package. This makes it possible that, even if some of memory cells included in any chip are defective, the memory device can normally function while using the chip including the defective memory cells. Suppose, however, that a chip including a control circuit and a plurality of memory cells has become defective due to, for example, a wiring failure of the control circuit, and the chip cannot function normally even by employing the redundancy technique. In such a case, the defective chip is no longer usable. While the defective chip can be replaced with a conforming one, it increases the cost for the layered chip package.
In order to reduce the possibility for a single layered chip package to include a defective chip, a possible approach is to reduce the number of chips included in each layered chip package. In such a case, a plurality of layered chip packages that include only conforming chips can be electrically connected to each other to form a memory device that includes a desired number of chips. This, however, gives rise to the problem of complicated wiring for electrically connecting the plurality of layered chip packages.